Mechanical seals are designed for use on a wide variety of machines having rotating shafts that pass through housings, such as pumps, agitators, blenders, separators, refiners, dryers and mixers. The function of the mechanical seal is to prevent leakage of pressurized fluids. In the mechanical seals to which this invention relates--sometimes referred to as a rotary face seal--sealing is achieved by arranging at least two durable sealing rings having extremely flat radially extending sealing faces axially adjacent to each other and concentrically disposed about the shaft so that the faces are in sealing contact. One ring is held stationary in the seal housing or gland while the other rotates with the shaft as part of a unit sometimes termed a rotary.
Repair or replacement of parts of such seals is difficult whenever inaccessibility of the outboard end of the shaft or the location of the machine make it impossible to slip the seal off the end of the shaft. In such situations, the machines themselves must be disassembled. To facilitate such repair or replacement of parts, use has been made of radially split sealing rings and other seal parts so that each ring may be removed from, and new rings reassembled within, the seal and about the shaft.
Typically, split rings are manufactured by cutting a whole ring into two segments. With cut rings, the cut faces of one ring segment thereby created are precisely lapped while discarding the other ring segment and mating the one segment with a segment from another whole ring of the same dimensions as a whole ring. Broken rings are also known and used. One type of broken ring, typically made of carbon, has irregular broken surfaces which permit self matching of the ring halves without lapping. On the other hand, broken rings formed by scoring and breaking rings made from silicon carbide or certain ceramic materials, tend to break quite cleanly and smoothly to provide substantially planar matching surfaces with only slight surface irregularities.
Mechanical seals of various designs utilizing split sealing rings are disclosed, for example, in U.S. Pat. Nos. 2,996,319; 3,101,200; 4,576,384; and G. B. 917,693. In addition, mechanical seals employing such split ring technology are available as articles of commerce from a number of manufacturers.
During installation of the split seal segments in the gland, precise alignment of the segments is essential. In the first place, proper alignment of the segments at the outset of installation minimizes the possibility of damage to the sealing ring through misalignment or incorrect contact between the co-engaging or abutting surfaces at the interfaces between the segments. This is especially important in the case of split sealing rings fabricated from carbon, silicon carbide or other similar ceramic or non-metallic materials, as segments made from such materials can become chipped or otherwise damaged if misaligned during assembly operations. Secondly, since the radially disposed sealing faces of the respective sealing rings must provide an extremely flat interface between these interacting faces, improper alignment, even if barely perceptible visually, can result in fluid leakage through the mechanical seal. This problem tends to be particularly troublesome in the case of silicon carbide or ceramic seals formed by scoring and breaking the ring to form substantially planar matching faces on the ring segments. And, in addition, if the ring segments can be placed in precise aligmnent easily and quickly, the overall assembly operation is greatly facilitated. While various alignment means for split rings have been designed or proposed heretofore, these have often required altering one or more of the co-engaging surfaces such as by boring, machining or otherwise creating holes or complex interlocking configurations in the seals at the co-engaging surfaces.